1. Field of the Invention
The present invention relates to a magnetic recording device.
2. Background Art
A bit size on a recording medium has become minute along with an increased recording capacity of a hard disk drive (HDD). However, when the bit size becomes minute, there arises a problem of loss of magnetization information due to thermal fluctuation. To solve such a problem and stably maintain a recording bit with an increased recording capacity, it is required to use a recording medium having a large coercive force (i.e., a large magnetic anisotropy).
An intensive recording magnetic field is required to record information on a recording medium having a large coercive force. In practice, however, the intensity of the recording magnetic field is limited because of narrowing of a recording head and limitation of utilizable magnetic materials. Accordingly, the coercive force of the recording medium is restricted by the intensity of the recording magnetic field generated by the recording head.
To achieve two conflicting aims of providing the thermal stability of the medium and the coercive force for easily recording information, methods for effectively lowering the coercive force of the recording medium using various auxiliary means only during recording have been suggested. Thermally assisted recording for recording information with use of heating means such as a magnetic head and laser is a typical example of such methods.
There is also a method for recording information while locally reducing the coercive force of the recording medium with use of a high frequency magnetic field as a recording magnetic field from a recording head. For example, JP Patent Publication (Kokai) No. 6-243527 discloses a technique of recording information while locally reducing a coercive force of a recording medium by subjecting the magnetic recording medium to joule heating or magnetic resonance heating by means of a high frequency magnetic field. In such a method for recording information by means of magnetic resonance between the high frequency magnetic field and a magnetic head magnetic field (hereinafter referred to as microwave assisted recording), a strong high frequency magnetic field, which is proportional to an anisotropy field of the recording medium, needs to be applied so as to reduce intensity of a magnetic reversal field.
X. Zhu and J. G. Zhu, “Bias-Field-Free Microwave Oscillator Driven by Perpendicularly Polarized Spin Current”, IEEE TRANSACTIONS ON MAGNETICS, P2670 VOL. 42, No. 10 (2006) discloses calculation results relating to a spin-torque oscillator that is free of a bias magnetic field from the outside.
J. G. Zhu, X. Zhu and Y. Tang, “Microwave Assisted Magnetic Recording”, IEEE TRANSACTIONS ON MAGNETICS, VOL. 44, NO. 1, pp. 125-131, JANUARY 2008 discloses a technique of recording information on a magnetic recording medium having a large magnetic anisotropy by disposing a field generation layer (FGL) that rapidly rotates based on spin torque near a magnetic recording medium adjacent to a main magnetic pole of a vertical magnetic head and generating a microwave (high frequency magnetic field).
Y. Wang, Y. Tang and J. G. Zhu, “Media damping constant and performance characteristics in microwave assisted magnetic recording with circular ac field”, JOURNAL OF APPLIED PHYSICS 105, 07B902 (2009) discloses a spin-torque oscillator that controls a rotational direction of an FGL with use of a magnetic field of a main magnetic pole adjacent to the FGL. Accordingly, microwave assisted magnetization reversal of a medium can be effectively achieved.
As a recording compensation method with use of a write current, write pre-compensation has been suggested. By such a method, a non-linear transition shift (NLTS), which is generated by interference of magnetization between bits due to an increased recording capacity, is compensated. By shifting a phase of a specified bit in recording information, a specified bit array of data, of which a peak shift has a problem, is adjusted.